In recent years, it has often been found desirable, indeed sometimes necessary, to obtain some type of indication as to the characteristics of ground, soil or underwater soil conditions including the rigidity, compaction or load bearing characteristics of such surfaces prior to initiating any one of a variety of types of operations on that surface. This becomes more of a concern when large areas need to be the basis of such operations or where foliage and surface growth prohibit easy or ready investigation of such surfaces by aerial means. Where there is no surface vegetation, aerial surveys may provide a sufficient degree of information for some types of operations. Likewise, where a relatively small area needs to be investigated, that can be done by simply having individuals move through the area and make on site investigations. In many other instances, however, on site or aerial means and some other means has to be found. Remote and otherwise inaccessible areas including both land and sea or river bottoms can only be effectively studied through more sosphisticated techniques. At other times it is desirable to determine what is flowing within closed prior art conduits.
Examples of such technqiues include Costello, et al, U.S. Pat. No. 3,298,222, Brooks, et al, U.S. Pat. No. 3,339,404, Payne, U.S. Pat. No. 3,623,359, Grice, U.S. Pat. No. 3,690,166, Vlasblom, U.S. Pat. No. 3,906,781 and Thompson, U.S. Pat. No. 4,007,633.
In Costello et al, the device is one that is used from a ship and allowed to be passed down through water at a constant velocity for impacting the bottom of a water course. An accelerometer or, a signal generating system, is connected by means of a cable directly connected to the ship and vehicle deceleration is monitored the results of which indicate the load bearing characteristics of the bottom surface.
Brooks et al was designed as a device for measuring and transmitting impact accelerations on the moon's surface. Impact acceleration data is compared with known acceleration time histories to determine physical properties of the soil being inspected including surface hardness , bearing strength and penetrability of the body. Brooks et al accomplishes this task by firing off individual penetrometers, the outputs from which are transmitted back to a receiving station on Earth.
Payne relates to a penetrometer also suited for use in determining the load characteristics of the lunar surface. The device was connected to the bottom of the lunar module itself; displacement of a pad member forced against the surface was measured over a given period of time to determine the capacity of the soil to support vertical loads. In particular, the probe included an improved pad structure that allowed that pad to be laterally displaced so that both vertical and lateral displacements could be detected and measured to determine the load bearing characteristics of the soil.
In Grice, an instrument platform was positioned on the bottom of a body of water and a device which burrowed its way into the soil was lowered into place and formed a passageway through which it moved. While various readings are taken with respect to conditions along the bore hole, it is not a penetrometer designed to make readings as it passes vertically through the soil or area being examined on the basis of a free fall drop.
Vlasblom discloses a soil probe or penetrometer designed to be pressed into soil that includes an annular, elastically deformable wall portion. Strain gauges are mounted on the interior surface thereof to sense pressure acting transversely to the axis of the tube. A water pressure gauge is also included and intergranular soil pressure is determined from the difference between the two pressures. In addition, there is an indication that insulated annular electrodes can be included for determining the electrical conductivity of the surrounding soil so that soil density information can derived. However, no further description is included and there is no structure set forth for accomplishing such a result.
Thompson is somewhat similar to Costello et al in that it is a device which is allowed to pass through water or the ocean until it strikes and imbeds itself in the ocean bottom to detect physical characteristics of the sea floor. However, rather than using a cable, the invention makes use of an acoustic signal which is transformed into an appropriate electrical analog signal with the data being sent from the penetrometer thus presenting a different way for transmitting signals from the penetrometer with respect to its deceleration as it comes to rest in the sea floor.
While the foregoing references describe various attempts in designing penetrometers, none are capable of producing a wide variety of measurements simultaneously to permit a number of determinations of soil characteristics beyond that connected with rigidity, compaction or load bearing characteristics or simple measurements indicating the presence or absence of water. Likewise, none are concerned with determining electrical resistance measurements in three orthogonal directions, determining stratification information, or measuring the depth of various mediums throughwhich the penetrometer passes. Additionally, none can distinguish between Newtonian and non-Newtonian fluids nor determine characteristics concerning the grains constituting the medium through which the penetrometer passes and comes to rest.
Further, the prior art has not recognized the desirability to track and retrack through the medium.